This invention relates to a composition and method for preserving wood and other cellulose based materials such as paper, particle board, textiles, rope, etc., against destructive organisms responsible for rot and decay, namely fungus and insects. More particularly, this invention relates to an organometal preservative composition, having insecticidal and fungicidal properties, in the form of an aqueous solution of a compound of metal ammonium complexes of certain specified dicarboxylic acids or mono, di or tricarboxylic hydroxy acids.
Metal compounds have long been recognized for their fungicidal properties. Copper sulfate was recommended for use in wood preservation as early as 1767 and patented for that purpose in England in 1937 by Margary. Since its initial use in the early 1800's copper sulfate has played a major role in the wood preserving industry. However, the use of copper sulfate as a wood preservative has two major disadvantages. First, copper sulfate does not become permanently fixed in the wood and is therefore prone to leaching. Secondly, copper alone is not an effective preservative against all forms of wood destroying organisms.
In the early 1940's, a new generation of water-borne preservatives with superior leach resistance was developed. These new preservative systems were based on copper plus the incorporation of chromium and/or arsenic. These preservative systems are known as chromated copper arsenate (CCA) and ammoniacal copper arsenate (ACA). These systems are effective preservatives and are the predominant water borne systems used in the wood preserving industry today.
The use of metal salts and organic acids as wood preservatives has been known since the early 1900's. During the creosote shortage of the mid-1940's, mixtures of naphthenic acids, derived from petroleum by-products, were combined with metal salts to form a series of compounds for wood preservation. One of these compounds was copper naphthenate. Copper naphthenate was formed by the reaction of copper salts with a group of organic acids known as cyclopentane carboxylic acids. Copper naphthenate is an oil-borne preservative system and while an effective preservative, it has a strong odor and because of its waxy nature, wood treated with this preservative is difficult to paint.
Additional antifungal water-borne preservative systems based on metal salts and fatty acids have since been developed. U.S. Pat. No. 4,061,500 describes a wood preservative effective against blue stain, containing a fatty acid of 6-11 carbon aroms, boric acid and an alkali compound in stoichiometric excess of the fatty acids. The incorporation of copper salts with straight chain fatty acids and fatty alcohols containing 6-12 carbon atoms per molecule is described in U.S. Pat. No. 4,001,400. Here, copper, zinc, nickel, cadmium and cobalt are combined with an ammoniacal fatty acid salt to provide a water-borne preservative system which is claimed to be effective against fungi mould and blue stain.
A process for preparing a homogeneous liquid composition comprising a cuprammonium complex of one or more monocarboxylic acids containing 1-4 carbon atoms per molecule is described in U.S. Pat. No. 4,175,090. These particular compositions are used as fungicides for treating wood, painting surfaces, fabrics and also to inhibit algal growth. U.S. Pat. No. 4,220,661 describes a preservative composition useful for preventing the growth of mould, bacteria and fungi comprising an aqueous solution of a complex salt of an ion selected from NH+.sub.4 and a Group I or Group II metal ion and one or more carboxylic acids selected from saturated and unsaturated aliphatic monocarboxylic acids containing from 2-8 carbon atoms.
U.S. Pat. No. 4,193,993 discloses a process for preparing an aqueous fungicidal preservative solution comprising a compound of a preservative metal, a branched-chain carboxylic acid having 6-20 carbon atoms or a dipentenemonocarboxylic acid or a dipentenedicarboxylic acid and ammonia and/or an ammonium compound. Similarly, U.S. Pat. No. 4,380,561 describes a preservative system comprising branched-chain aliphatic carboxylic acids containing 6-20 carbon atoms or their alkali or ammonium salts. This composition is particularly suitable for the short term protection of wood against sapstain and mould fungi, but not from attack by insects.
It has long been desirable to produce wood products that are aesthetically acceptable to the public, yet preserved from the destructive agencies of wood. Preserved wood is desirable for the home, and is used in the siding, fencing and decking industry. Unfortunately, many of the fatty acid preservative solutions described above are effective only against fungal and bacterial attack, and do little to protect the wood from attack by insects, and particularly termites. Accordingly, it has now been discovered that by changing the organic acid substituent of prior used preservative compositions from a normal fatty acid to a dicarboxylic acid or to a mono, di or tricarboxylic hydroxy acid, the resulting preservative will be effective against both fungal and insect attack.